1. Field of the Invention
The present invention relates to a wireless communication system. More particularly, the present invention relates to an apparatus and method for controlling transmission power of an uplink sounding signal in a wireless communication system.
2. Description of the Related Art
A conventional communication system has been developed with a focus on a voice call service. Recently, communication systems are being developed in order to provide data service and various multimedia services, in addition to the voice call service. However, since the conventional communication system provides only the voice call, the conventional communication system has a narrow bandwidth and expensive fees, and does not satisfy increased demands of users. Additionally, due to developments in the communication industry and user demands for Internet service, a need for an efficient communication system that provides Internet service has significantly increased. Accordingly, a broadband wireless communication system has been considered for efficiently providing Internet service.
The broadband wireless communication system is based on Orthogonal Frequency Division Multiplexing/Orthogonal Frequency Division Multiple Access (OFDM/OFDMA) and is able to archive a fast data transmission by transmitting signals using a plurality of sub-carriers in a physical channel. A radio access scheme of the broadband wireless communication system is being standardized in an Institute of Electrical and Electronics Engineers (IEEE) 802.16 standard.
In the broadband wireless communication system based on the OFDM/OFDMA, higher uplink transmit power causes interference to other terminals and adjacent cells, and lower uplink transmit power decreases a received power of a Base Station (BS). Accordingly, power control is needed to satisfy required Carrier to Interference and Noise Ratio (CINR) in which research to find an effective uplink power control scheme is presently ongoing. Referring to the IEEE 802.16e standard, the uplink power control is classified into an Open Loop (OL) power control and a Closed Loop (CL) power control. The OL power control is a scheme that a Mobile Station (MS) estimates a downlink path loss and determines uplink power under an assumption where a path loss at an uplink channel and a path loss at a downlink channel are identical. The CL power control is a scheme where a BS controls uplink power of an MS.
Although the IEEE 802.16e standard defines the OL power control and the CL power control, the power control is applied to data transmission. However, a signal for uplink channel estimation, i.e., a sounding signal, pilot signals, a preamble signal and the like, is not defined. In other words, the IEEE 802.16e standard states a plurality of required CINR values for each Modulation and Coding Scheme (MCS) level regarding the data transmission, but states only a single CINR value for the sounding signal as shown in Table 1 below.
TABLE 1Modulation/FEC rateNormalized C/NSounding transmission9
As aforementioned, only one CINR value is stated for the sounding signal. In consequence, a uniform target CINR value is required to transmit the sounding signal without reference to a status of an MS, i.e., a location, a channel condition and the like. Therefore, noise and interference levels are increased in the overall communication system.
Therefore a need exists for an apparatus and method for controlling power of an uplink sounding signal in a wireless communication system in order to decrease the level of noise and interference.